1. Field of the Invention
The present invention relates generally to methods and apparatus using ultrasonics in the field of medical technology and, more particularly, to an applicator for performing presurgical and surgical procedures using high-intensity focused ultrasound.
2. Description of Related Art
Therapeutic ultrasound refers to the use of high intensity ultrasonic waves to induce changes in living tissue state through both thermal effectsxe2x80x94referred to in the art as induced hyperthermiaxe2x80x94and mechanical effectsxe2x80x94induced cavitation. High frequency ultrasound has been employed in both hyperthermic and cavitational medical applications, whereas low frequency ultrasound has been used principally for its cavitation effect. Diagnostic medical ultrasonic imaging is well known, for example, in the common use of sonograms for fetal examination. Various aspects of diagnostic and therapeutic ultrasound methodologies and apparatus are discussed in depth in an article by G. ter Haar, Ultrasound Focal Beam Surgery, Ultrasound in Med. and Biol., Vol. 21, No. 9, pp. 1089-1100, 1995, and the IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, November. 1996, Vol. 43, No. 6 (ISSN 0885-3010), incorporated herein by reference. Particular methods and apparatus for medical applications of high intensity focused ultrasound, for example, for hemostasis and tissue necrotization, are the subject of pending U.S. patent application Ser. No. 08/961,972 now U.S. Pat. No. 6,007,499 issued Dec. 28, 1999 (assigned to the common assignee of the present invention and incorporated herein by reference).
In high-intensity focused ultrasound (HIFU) hyperthermia treatments, intensity of ultrasonic waves generated by a highly focused transducer increases from the source to the region of focus, or focal region, where it can cause a high temperature effect, e.g. to 98xc2x0 Centigrade. The absorption of the ultrasonic energy at the focus induces a sudden temperature rise of targeted tissuexe2x80x94as high as one to two hundred degrees Kelvin/secondxe2x80x94which causes the irreversible ablation of the target volume of cells. Thus, for example, HIFU hyperthermia treatments can cause necrotization of or around an internal lesion without damage to the intermediate tissues. The focal region dimensions are referred to as the depth of field, and the distance from the transducer to the center point of the focal region is referred to as the depth of focus. In the main, ultrasound is a promising non-invasive surgical technique because the ultrasonic waves provide a non-effective penetration of intervening tissues, yet with sufficiently low attenuation to deliver energy to a small focal target volume. Currently there is no other known modality that offers noninvasive, deep, localized focusing of non-ionizing radiation for therapeutic purposes. Thus, ultrasonic treatment has a great advantage over microwave and radioactive therapeutic treatment techniques.
Blood loss due to internal or external bleeding in trauma patients and hemorrhage in surgery is a major form of casualty. Hemostasis is currently performed using intense heat, electrocautery, lasers, embolization, or application of extreme cold. HIFU offers an alternative as the sonic energy can be focused to a distant point within the body without damage to intervening tissue, allowing non-invasive hemostasis.
Various embodiments of ultrasonic applicators or probes generally include a manipulable transducer, having a power supply and electrical matching circuitry for driving the transducer, and a coupling device for guiding the ultrasonic energy from the face of the transducer to the site of the tissue to be treated. Coupling devices consist generally of a hollow members filled with water. Water provides excellent coupling of acoustic energy into tissue because of the similarity in their acoustic impedances; both media have a characteristic impedance of approximately 1.5 megarayls. However, it has been found that there are disadvantages in the use of the water-filled coupling for medical procedures. At the high intensities at which the device is operated, the water in the coupling device is prone to cavitation; the bubbles produced are disruptive to the ultrasound energy. Thus, degassed water must be used to reduce the chance for cavitation. Furthermore, a water-filled device in a surgical environment is very difficult to sterilize and it must be refilled with sanitary, degassed water each time it is used. If the coupling device ruptures, water leaks out and blood from the patient leaks in, further complicating surgical conditions. Extra tubes and equipment are required to pump and circulate the water within the cone, making for a complicated and cumbersome apparatus difficult to optimize for emergency rescue situations.
In the use of HIFU, another problem is that driving transducers at high voltage generates heat. The frequencies required lead to the need for thin, fragile transducer elements. Thus, a HIFU medical instrument has inherent design problems which can make an HIFU instrument hard to use manually and.where overheating can cause transducer failure.
Thus, there is a need for improved ultrasound-to-tissue coupling devices. A simple, effective coupling device to replace the water-filled coupling devices must be easily sterilized and prepared for use or quickly refittable with a prepackaged, sterile replacement. A solid-state coupling device must additionally resolve the existence of inherent shear modes which complicate and adversely affect the transmission of longitudinal mode ultrasonic energy, the more effective form for most therapeutic type medical procedures. Furthermore, there is a need for improving ultrasonic applicators amenable for use in catheteric medical procedures.
In one of its basic aspects, the present invention provides a method for producing a therapeutic, high intensity, focused, ultrasonic energy pattern in living tissue. The method includes the steps of: focusing a beam of ultrasound through a solid material such that it converges towards a focal point in the solid material; truncating the solid material behind the focal point; refocusing the beam with a lens at the focal point to provide a predetermined focal region externally of the solid material; and coupling the lens to the living tissue such that the focal region is directed to a target point within the living tissue. More specifically, the method includes generating a sonic wave with a concave transducer; coupling the transducer to a solid coupler, the coupler having a predetermined geometric apex, wherein the sonic wave is transmitted through the coupler within a predetermined external boundary layer of the coupler; prior to the wave reaching the apex, subjecting the wave to a lens for redirecting the sonic wave; and coupling the lens directly to the living tissue such that the focal region is directed to a target within the living tissue. The method also includes tailoring transducer geometry and coupler geometry and transducer generating frequency to specific therapeutic tasks.
In another basic aspect, the present invention provides a high intensity focused ultrasonic applicator device for performing medical procedures, including: at least one transducer for generating a focused ultrasound beam; mounted to the transducer, a coupler, or applicator, which transmits the beam towards a focal point therein; the coupler is formed of a solid material; and a lens mechanism, located between the transducer and the focal point, for redirecting the beam.
In another basic aspect, the present invention provides a high intensity focused ultrasound medical instrument, including: a handle; mounted to the handle, a housing including a cavity; a transducer having a substantially concave geometry for providing a focused ultrasonic beam from a transducer concave frontside, wherein the transducer is mounted in the housing such that a transducer backside thereof is open to the cavity; and an ultrasound applicator, having an applicator backside having a convex geometry substantially identical to the concave geometry of the transducer; the applicator is nested with the transducer with the transducer concave frontside substantially adjacent the applicator backside; the applicator being of a solid material having a truncated tip such that the tip forms a lens for refocusing the beam; and the handle is adapted for providing a conduit for coupling power and a cooling medium to the cavity.
It is an advantage of the present invention that it provides improved ultrasonic coupling to living tissue.
It is an advantage of the present invention that it provides surgical means for achieving rapid hemostasis in an ultrasonic surgical instrument that can be tailored to access difficult areas.
It is an advantage of the present invention that it provides a practical high intensity focused ultrasound applicator that is easily usable and virtually fool proof in surgery.
It is another advantage of the present invention that is provides a medical applicator of high durability which is easily cleaned and sterilized.
It is another advantage of the present invention that it is adaptable to sterile packaging of quick-fit replacement elements.
It is a further advantage of the present invention that it requires no special maintenance for surgical environments.
It is a further advantage of the present invention that it is easily held and used by the surgeon in cauterizing and treating tissue.
It is still another advantage of the present invention that it is easily manufactured using conventional processes.
It is still another advantage that it provides a surgical tool having a shape that provides a visual pointer towards where the therapeutic energy will be.
It is still another advantage of the present invention that it can incorporate with secondary energy sources, measuring tools, diagnostic or therapy instruments, and the like.
It is yet another advantage that it can be implemented in a portable, battery-powered embodiment for both surgery and emergency trauma remote site use.
It is yet another advantage of the present invention that it can provide rapid treatment to a large tissue surface area.
It is yet another advantage of the present invention that the apparatus can be used in a Doppler ultrasound mode to aid in positioning the apparatus with respect to a hemorrhage site for accurate application of HIFU therapy.
Other objects, features and advantages of the present invention will become apparent upon consideration of the following explanation and the accompanying drawings, in which like reference designations represent like features throughout the drawings.